late 14c., "act of giving way and falling down," from Old French ruine "a collapse" (14c.), and directly from Latin ruina "a collapse, a rushing down, a tumbling down" (source also of Spanish ruina, Italian rovina), related to ruere "to rush, fall violently, collapse," from PIE *reue- (2) "to smash, knock down, tear out, dig up" (see rough (adj.)). Meaning "complete destruction of anything" is from 1670s. Ruins "remains of a decayed building or town" is from mid-15c.; the same sense was in the Latin plural noun.
1580s (transitive), from ruin (n.). Intransitive sense "fall into ruin" is from c. 1600. Financial sense is attested from 1660. Related: Ruined; ruining.